Method of making electric heating elements



June 11, 1968 A. c. 80665 3,387,363

METHOD OF MAKING ELECTRIC HEATING ELEMENTS Filed Jan. 13, 1965 INVENTOR. ALBEN (3 5:26:35

United States Patent "ice 3,387,363 METHOD OF MAKING ELECTRIC HEATING ELEMENTS Alben C. Boggs, Pittsburgh, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa. Filed Jan. 13, 1965, Ser. No. 425,168 1 Claim. (Cl. 29-619) ABSTRACT OF THE DISCLOSURE Hermetically sealing an end of a sheathed electric resistance heating element by use of a pre-formed fusible member disposed within a sealing sleeve.

The present invention relates to electric heating elements, more particularly to hermetically sealed, sheathed electric resistance heating elements and methods of making the same, and the principal object of the invention is to provide new and improved methods and articles of the character described.

The present invention is an improvement on the construction in US. Letters Patent No. 3,122,718, issued to me on Feb. 25, 1964. Briefly, by means of a novel structure and method, the improvement provides a hermetically sealed, tubular sheathed electric resistance heating element whose breakdown voltage remains high to insure against premature failure. This is accomplished in a relatively simple manner with consequent economies in manufacturing cost.

In the drawing accompanying this specification and forming a part of this application there is shown, for purpose of illustration, an embodiment which the invention may assume, and in this drawing:

FIGURE 1 is a fragmentary, broken view, in longitudinal section of a heating element embodying my invention,

FIGURE 2 is a fragmentary elevational view of a coil of fusible wire used in the method of my invention,

FIGURE 3 is a side elevation of a portion of the con struction used in the embodiment shown in FIGURE 1, a portion being broken away to better illustrate construction,

FIGURE 4 is an end view of the portion shown in FIGURE 3, and

FIGURE 5 is an elevational view, partly in section, showing a step in the assembly of the embodiment.

With reference to FIGURE 1, there is fragmentarily illustrated one end of an electric resistance element of the well-known type having a tubular metallic sheath 1i enclosing a coiled resistor conductor 11 which terminates short of the sheath end. A terminal conductor pin 12 is mechanically and electrically connected to the end of the resistor conductor 11 and projects axially outwardly of and beyond the open end of the sheath for connection to a source of electrical energy.

The sheath 10 is filled with highly compacted con ductive material 14, such as granular refractory material, which maintains the resistor conductor and terminal pin centered within the sheath. For a purpose to appear, the material 14 preferably terminates short of the end of the sheath to form a recess 15 thereat.

Substantially filling the sheath recess 15 is a body of cement-like, dielectric material 16 in which is embedded one end of a dense, dielectric ceramic sleeve 17 made, for example, of porcelain. The terminal pin 12 passes through the sleeve as best seen in FIGURE 1. The dielectric sleeve is cylindrical and of one piece construction and has one end 18 of reduced diameter to form a peripheral space 19 with the adjoining end of the sheath.

The means for hermetically sealing the heating element 3,337,353 Patented June 11, 1968 thus far described comprises an assembly including the dielectric sleeve 17, a metal sleeve 20 at one end and a metal ferrule or cap 21 at the other end. The metal sleeve 20 and ferrule 21 are hermetically sealed to the exterior surface of the cylindrical dielectric sleeve in the axially spaced relation shown in FIGURE 1, the hermetic sealing being accomplished in any suitable manner, as by cement or the like, and each projects beyond the respective end of the main portion of the dielectric sleeve.

The projecting portion of the metal sleeve 20 has a transverse shape complementary to the adjoining shape of the sheath 10. In the disclosed embodiment, the sheath is round in cross-section and therefore the metal sleeve is also round with an internal diameter to have a slip fit with the end portion of the sheath. The free end of the metal sleeve 20 is belled, as shown at 22, to form a peripheral space 23 with the sheath end portion. The projecting portion of the ferrule 21 is necked down, as at 24, and may be externally threaded, as shown, to facilitate its connection to a source of electrical energy. The dielectric sleeve 17, the metal sleeve 20 and the ferrule 21 form a sub-assembly, as shown in FTGURE 3, which may be manufactured separately.

In assembling the heating element illustrated in FIG- URE 1, the recess 15 is substantially filled with the cement 16 which is in a plastic state. The sub-assembly of FIGURE 3 is then slid over the terminal pin 12 with the metal sleeve 20 finally telescoping over the adjoining end of the sheath 10 and with the reduced end 18 of the dielectric sleeve entering the plastic cement and acting like a piston to extrude the cement so that the latter intimately fills all the space between adjoining parts, as seen in FIGURE 1. The extremity of the sheath end may conveniently abut the shoulder 25 formed by the necked down portion 18 of the dielectric sleeve 17 to limit movement of the metal sleeve 20 over the sheath end.

The free end of the terminal pin 12 preferably extends a slight amount beyond the adjoining end of the ferrule 24, and a hermetically sealed joint 26 is formed, such as by silver solder. A fusible member is disposed and held within the space 23 and the assembly may be subjected to a heating operation to melt the fusible member and establish a hermetic bond between the belled end 22 and they adjoining portion of the sheath.

At the present time it is preferred to wind a silver solder wire (Easyflo alloy, for example) into a coil 28, as shown in FIGURE 2, of an external diameter to snugly fit within the belled portion 22, and to cut the convolutions of the coil into individual rings 29 (a ring being shown in FIGURES 3, 4 and 5). The ring is disposed within the belled portion and is prevented from movement too far into the metal sleeve by abutment with the bottom wall of the belled portion. To hold the ring 29 from dropping out of the belled portion 22, the latter is formed with one or more shoulders, and in the present embodiment the shoulders are formed by inwardly indenting the edge margin of the belled portion, as shown at 30, at a plurality of places.

Thus, the assembly may be disposed in vertical position with the belled portion opening downwardly, as seen in FIGURE 5. Sufficient heat is then applied, preferably localized in the vicinity of the belled portion, to melt the fusible ring 29 and establish a peripheral hermetic bond between the belled portion and the sheath end. For production purposes, it has been found preferable to use a single turn induction coil 31 surrounding the sheath and positioned slightly below the lower edge of the belled portion, as shown in FIG. 5.

In view of the foregoing it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention and it will also be ap- Q) parent to those skilled in the art that the embodiment herein described may be variously changed and modified, Without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described; hence it will be appreciated that the herein disclosed embodiment is illustrative only, and that my invention is not limited thereto.

I claim:

1. In an electric resistance heating element having a tubular metallic sheath, the method of securing an end member over an end of said sheath, said member having a metallic sleeve with a belled open end of an internal diameter slightly larger than the external diameter of said sheath end, said method comprising indenting said belled end radially inwardly at a plurality of peripherally spaced places to form peripherally spaced shoulders spaced from the bottom wall of said belled end, holding a fusible ring between said shoulders and said bottom Wall, the ring having an internal diameter to fit over said sheath end and an external diameter to freely fit within said sleeve, the shoulders holding said ring from easily coming out of the belled end of said sleeve, disposing said belled end and said fusible ring over and around said sheath end, holding the foregoing assembly upright With said sheath lowermost, and disposing an induction coil around said sheath end in the vicinity of said belled end and energizing said coil to produce heat localized at said sheath end to melt said fusible ring and establish a bond-between adjoining peripheral surfaces of said sheath and belled end.

References Cited UNITED STATES PATENTS 2,471,650 5/1949 Pandolfi.

CHARLIE T. MOON, Primary Examiner. JOHN F. CAMPBELL, Examiner.

J. CLINE, Assistant Examiner. 

